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IP subnet calculator

Type an address with its prefix or mask to see the network, its usable range and masks. Split it into smaller subnets, or look up any prefix in the reference tables.

Network51.2.128.0/17
Usable hosts32,766
Subnet mask255.255.128.0
Addresses32,768
Network address
51.2.128.0
Broadcast address
51.2.255.255
First usable
51.2.128.1
Last usable
51.2.255.254
Usable hosts
32,766 (32,768 less the network and broadcast addresses)
Subnet mask
255.255.128.0
Wildcard mask
0.0.127.255 (Cisco ACLs, OSPF)
Prefix length
/17
Type
Public public
Old class
A (default /8)
As numbers
Hex 33028000 · Integer 855801856 to 855834623
Reverse DNS zones
128.2.51.in-addr.arpa
129.2.51.in-addr.arpa
130.2.51.in-addr.arpa
131.2.51.in-addr.arpa
132.2.51.in-addr.arpa
133.2.51.in-addr.arpa
134.2.51.in-addr.arpa
135.2.51.in-addr.arpa
136.2.51.in-addr.arpa
137.2.51.in-addr.arpa
138.2.51.in-addr.arpa
139.2.51.in-addr.arpa
140.2.51.in-addr.arpa
141.2.51.in-addr.arpa
142.2.51.in-addr.arpa
143.2.51.in-addr.arpa
and 112 more
/17 is not on a 8-bit boundary, so it takes 128 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00110011.00000010.10000000.0000000051.2.128.0
Subnet mask11111111.11111111.10000000.00000000255.255.128.0
Network00110011.00000010.10000000.0000000051.2.128.0
Broadcast00110011.00000010.11111111.1111111151.2.255.255
Split into smaller subnets/24
/18 (2)/19 (4)/20 (8)/21 (16)/22 (32)/23 (64)/24 (128)/25 (256)/26 (512)/27 (1,024)/28 (2,048)/29 (4,096)

51.2.128.0/17 makes 128 subnets of /24.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
151.2.128.0/2451.2.128.1 to 51.2.128.25451.2.128.255254
251.2.129.0/2451.2.129.1 to 51.2.129.25451.2.129.255254
351.2.130.0/2451.2.130.1 to 51.2.130.25451.2.130.255254
451.2.131.0/2451.2.131.1 to 51.2.131.25451.2.131.255254
551.2.132.0/2451.2.132.1 to 51.2.132.25451.2.132.255254
651.2.133.0/2451.2.133.1 to 51.2.133.25451.2.133.255254
751.2.134.0/2451.2.134.1 to 51.2.134.25451.2.134.255254
851.2.135.0/2451.2.135.1 to 51.2.135.25451.2.135.255254
951.2.136.0/2451.2.136.1 to 51.2.136.25451.2.136.255254
1051.2.137.0/2451.2.137.1 to 51.2.137.25451.2.137.255254
1151.2.138.0/2451.2.138.1 to 51.2.138.25451.2.138.255254
1251.2.139.0/2451.2.139.1 to 51.2.139.25451.2.139.255254
1351.2.140.0/2451.2.140.1 to 51.2.140.25451.2.140.255254
1451.2.141.0/2451.2.141.1 to 51.2.141.25451.2.141.255254
1551.2.142.0/2451.2.142.1 to 51.2.142.25451.2.142.255254
1651.2.143.0/2451.2.143.1 to 51.2.143.25451.2.143.255254
1751.2.144.0/2451.2.144.1 to 51.2.144.25451.2.144.255254
1851.2.145.0/2451.2.145.1 to 51.2.145.25451.2.145.255254
1951.2.146.0/2451.2.146.1 to 51.2.146.25451.2.146.255254
2051.2.147.0/2451.2.147.1 to 51.2.147.25451.2.147.255254
2151.2.148.0/2451.2.148.1 to 51.2.148.25451.2.148.255254
2251.2.149.0/2451.2.149.1 to 51.2.149.25451.2.149.255254
2351.2.150.0/2451.2.150.1 to 51.2.150.25451.2.150.255254
2451.2.151.0/2451.2.151.1 to 51.2.151.25451.2.151.255254
2551.2.152.0/2451.2.152.1 to 51.2.152.25451.2.152.255254
2651.2.153.0/2451.2.153.1 to 51.2.153.25451.2.153.255254
2751.2.154.0/2451.2.154.1 to 51.2.154.25451.2.154.255254
2851.2.155.0/2451.2.155.1 to 51.2.155.25451.2.155.255254
2951.2.156.0/2451.2.156.1 to 51.2.156.25451.2.156.255254
3051.2.157.0/2451.2.157.1 to 51.2.157.25451.2.157.255254
3151.2.158.0/2451.2.158.1 to 51.2.158.25451.2.158.255254
3251.2.159.0/2451.2.159.1 to 51.2.159.25451.2.159.255254
3351.2.160.0/2451.2.160.1 to 51.2.160.25451.2.160.255254
3451.2.161.0/2451.2.161.1 to 51.2.161.25451.2.161.255254
3551.2.162.0/2451.2.162.1 to 51.2.162.25451.2.162.255254
3651.2.163.0/2451.2.163.1 to 51.2.163.25451.2.163.255254
3751.2.164.0/2451.2.164.1 to 51.2.164.25451.2.164.255254
3851.2.165.0/2451.2.165.1 to 51.2.165.25451.2.165.255254
3951.2.166.0/2451.2.166.1 to 51.2.166.25451.2.166.255254
4051.2.167.0/2451.2.167.1 to 51.2.167.25451.2.167.255254
4151.2.168.0/2451.2.168.1 to 51.2.168.25451.2.168.255254
4251.2.169.0/2451.2.169.1 to 51.2.169.25451.2.169.255254
4351.2.170.0/2451.2.170.1 to 51.2.170.25451.2.170.255254
4451.2.171.0/2451.2.171.1 to 51.2.171.25451.2.171.255254
4551.2.172.0/2451.2.172.1 to 51.2.172.25451.2.172.255254
4651.2.173.0/2451.2.173.1 to 51.2.173.25451.2.173.255254
4751.2.174.0/2451.2.174.1 to 51.2.174.25451.2.174.255254
4851.2.175.0/2451.2.175.1 to 51.2.175.25451.2.175.255254
4951.2.176.0/2451.2.176.1 to 51.2.176.25451.2.176.255254
5051.2.177.0/2451.2.177.1 to 51.2.177.25451.2.177.255254
5151.2.178.0/2451.2.178.1 to 51.2.178.25451.2.178.255254
5251.2.179.0/2451.2.179.1 to 51.2.179.25451.2.179.255254
5351.2.180.0/2451.2.180.1 to 51.2.180.25451.2.180.255254
5451.2.181.0/2451.2.181.1 to 51.2.181.25451.2.181.255254
5551.2.182.0/2451.2.182.1 to 51.2.182.25451.2.182.255254
5651.2.183.0/2451.2.183.1 to 51.2.183.25451.2.183.255254
5751.2.184.0/2451.2.184.1 to 51.2.184.25451.2.184.255254
5851.2.185.0/2451.2.185.1 to 51.2.185.25451.2.185.255254
5951.2.186.0/2451.2.186.1 to 51.2.186.25451.2.186.255254
6051.2.187.0/2451.2.187.1 to 51.2.187.25451.2.187.255254
6151.2.188.0/2451.2.188.1 to 51.2.188.25451.2.188.255254
6251.2.189.0/2451.2.189.1 to 51.2.189.25451.2.189.255254
6351.2.190.0/2451.2.190.1 to 51.2.190.25451.2.190.255254
6451.2.191.0/2451.2.191.1 to 51.2.191.25451.2.191.255254
6551.2.192.0/2451.2.192.1 to 51.2.192.25451.2.192.255254
6651.2.193.0/2451.2.193.1 to 51.2.193.25451.2.193.255254
6751.2.194.0/2451.2.194.1 to 51.2.194.25451.2.194.255254
6851.2.195.0/2451.2.195.1 to 51.2.195.25451.2.195.255254
6951.2.196.0/2451.2.196.1 to 51.2.196.25451.2.196.255254
7051.2.197.0/2451.2.197.1 to 51.2.197.25451.2.197.255254
7151.2.198.0/2451.2.198.1 to 51.2.198.25451.2.198.255254
7251.2.199.0/2451.2.199.1 to 51.2.199.25451.2.199.255254
7351.2.200.0/2451.2.200.1 to 51.2.200.25451.2.200.255254
7451.2.201.0/2451.2.201.1 to 51.2.201.25451.2.201.255254
7551.2.202.0/2451.2.202.1 to 51.2.202.25451.2.202.255254
7651.2.203.0/2451.2.203.1 to 51.2.203.25451.2.203.255254
7751.2.204.0/2451.2.204.1 to 51.2.204.25451.2.204.255254
7851.2.205.0/2451.2.205.1 to 51.2.205.25451.2.205.255254
7951.2.206.0/2451.2.206.1 to 51.2.206.25451.2.206.255254
8051.2.207.0/2451.2.207.1 to 51.2.207.25451.2.207.255254
8151.2.208.0/2451.2.208.1 to 51.2.208.25451.2.208.255254
8251.2.209.0/2451.2.209.1 to 51.2.209.25451.2.209.255254
8351.2.210.0/2451.2.210.1 to 51.2.210.25451.2.210.255254
8451.2.211.0/2451.2.211.1 to 51.2.211.25451.2.211.255254
8551.2.212.0/2451.2.212.1 to 51.2.212.25451.2.212.255254
8651.2.213.0/2451.2.213.1 to 51.2.213.25451.2.213.255254
8751.2.214.0/2451.2.214.1 to 51.2.214.25451.2.214.255254
8851.2.215.0/2451.2.215.1 to 51.2.215.25451.2.215.255254
8951.2.216.0/2451.2.216.1 to 51.2.216.25451.2.216.255254
9051.2.217.0/2451.2.217.1 to 51.2.217.25451.2.217.255254
9151.2.218.0/2451.2.218.1 to 51.2.218.25451.2.218.255254
9251.2.219.0/2451.2.219.1 to 51.2.219.25451.2.219.255254
9351.2.220.0/2451.2.220.1 to 51.2.220.25451.2.220.255254
9451.2.221.0/2451.2.221.1 to 51.2.221.25451.2.221.255254
9551.2.222.0/2451.2.222.1 to 51.2.222.25451.2.222.255254
9651.2.223.0/2451.2.223.1 to 51.2.223.25451.2.223.255254
9751.2.224.0/2451.2.224.1 to 51.2.224.25451.2.224.255254
9851.2.225.0/2451.2.225.1 to 51.2.225.25451.2.225.255254
9951.2.226.0/2451.2.226.1 to 51.2.226.25451.2.226.255254
10051.2.227.0/2451.2.227.1 to 51.2.227.25451.2.227.255254
10151.2.228.0/2451.2.228.1 to 51.2.228.25451.2.228.255254
10251.2.229.0/2451.2.229.1 to 51.2.229.25451.2.229.255254
10351.2.230.0/2451.2.230.1 to 51.2.230.25451.2.230.255254
10451.2.231.0/2451.2.231.1 to 51.2.231.25451.2.231.255254
10551.2.232.0/2451.2.232.1 to 51.2.232.25451.2.232.255254
10651.2.233.0/2451.2.233.1 to 51.2.233.25451.2.233.255254
10751.2.234.0/2451.2.234.1 to 51.2.234.25451.2.234.255254
10851.2.235.0/2451.2.235.1 to 51.2.235.25451.2.235.255254
10951.2.236.0/2451.2.236.1 to 51.2.236.25451.2.236.255254
11051.2.237.0/2451.2.237.1 to 51.2.237.25451.2.237.255254
11151.2.238.0/2451.2.238.1 to 51.2.238.25451.2.238.255254
11251.2.239.0/2451.2.239.1 to 51.2.239.25451.2.239.255254
11351.2.240.0/2451.2.240.1 to 51.2.240.25451.2.240.255254
11451.2.241.0/2451.2.241.1 to 51.2.241.25451.2.241.255254
11551.2.242.0/2451.2.242.1 to 51.2.242.25451.2.242.255254
11651.2.243.0/2451.2.243.1 to 51.2.243.25451.2.243.255254
11751.2.244.0/2451.2.244.1 to 51.2.244.25451.2.244.255254
11851.2.245.0/2451.2.245.1 to 51.2.245.25451.2.245.255254
11951.2.246.0/2451.2.246.1 to 51.2.246.25451.2.246.255254
12051.2.247.0/2451.2.247.1 to 51.2.247.25451.2.247.255254
12151.2.248.0/2451.2.248.1 to 51.2.248.25451.2.248.255254
12251.2.249.0/2451.2.249.1 to 51.2.249.25451.2.249.255254
12351.2.250.0/2451.2.250.1 to 51.2.250.25451.2.250.255254
12451.2.251.0/2451.2.251.1 to 51.2.251.25451.2.251.255254
12551.2.252.0/2451.2.252.1 to 51.2.252.25451.2.252.255254
12651.2.253.0/2451.2.253.1 to 51.2.253.25451.2.253.255254
12751.2.254.0/2451.2.254.1 to 51.2.254.25451.2.254.255254
12851.2.255.0/2451.2.255.1 to 51.2.255.25451.2.255.255254

IPv4 CIDR reference (/0 to /32)

IPv4 prefix lengths
PrefixSubnet maskWildcardAddressesUsable hostsSizeTypical use
/00.0.0.0255.255.255.2554,294,967,2964,294,967,29416,777,216 × /24
/1128.0.0.0127.255.255.2552,147,483,6482,147,483,6468,388,608 × /24
/2192.0.0.063.255.255.2551,073,741,8241,073,741,8224,194,304 × /24
/3224.0.0.031.255.255.255536,870,912536,870,9102,097,152 × /24
/4240.0.0.015.255.255.255268,435,456268,435,4541,048,576 × /24
/5248.0.0.07.255.255.255134,217,728134,217,726524,288 × /24
/6252.0.0.03.255.255.25567,108,86467,108,862262,144 × /24
/7254.0.0.01.255.255.25533,554,43233,554,430131,072 × /24
/8255.0.0.00.255.255.25516,777,21616,777,21465,536 × /24Old class A; 10.0.0.0/8
/9255.128.0.00.127.255.2558,388,6088,388,60632,768 × /24
/10255.192.0.00.63.255.2554,194,3044,194,30216,384 × /24
/11255.224.0.00.31.255.2552,097,1522,097,1508,192 × /24
/12255.240.0.00.15.255.2551,048,5761,048,5744,096 × /24172.16.0.0/12
/13255.248.0.00.7.255.255524,288524,2862,048 × /24
/14255.252.0.00.3.255.255262,144262,1421,024 × /24
/15255.254.0.00.1.255.255131,072131,070512 × /24
/16255.255.0.00.0.255.25565,53665,534256 × /24Old class B; 192.168.0.0/16
/17255.255.128.00.0.127.25532,76832,766128 × /24
/18255.255.192.00.0.63.25516,38416,38264 × /24
/19255.255.224.00.0.31.2558,1928,19032 × /24
/20255.255.240.00.0.15.2554,0964,09416 × /24
/21255.255.248.00.0.7.2552,0482,0468 × /24
/22255.255.252.00.0.3.2551,0241,0224 × /24Large office or guest Wi-Fi (1,022 hosts)
/23255.255.254.00.0.1.2555125102 × /24Larger office LAN (510 hosts)
/24255.255.255.00.0.0.2552562541 × /24Typical office LAN (old class C)
/25255.255.255.1280.0.0.1271281261/2 of a /24Smaller LAN or VLAN
/26255.255.255.1920.0.0.6364621/4 of a /24Smaller LAN or VLAN
/27255.255.255.2240.0.0.3132301/8 of a /24Small VLAN, phones, cameras
/28255.255.255.2400.0.0.1516141/16 of a /24Small VLAN, phones, cameras
/29255.255.255.2480.0.0.7861/32 of a /24Small fixed public block (5 usable)
/30255.255.255.2520.0.0.3421/64 of a /24Point-to-point (old style)
/31255.255.255.2540.0.0.1221/128 of a /24Point-to-point link (RFC 3021)
/32255.255.255.2550.0.0.0111/256 of a /24One host

IPv6 prefix reference

IPv6 prefix lengths
PrefixAddresses/64 LANs/48 sitesNibbleTypical use
/342,535,295,865,117,307,932,921,825,928,971,026,432 (2^125)2,305,843,009,213,693,95235,184,372,088,832NoAll global unicast (2000::/3)
/165,192,296,858,534,827,628,530,496,329,220,096 (2^112)281,474,976,710,6564,294,967,296Yes
/20324,518,553,658,426,726,783,156,020,576,256 (2^108)17,592,186,044,416268,435,456YesLarge provider allocation (RIPE minimum for some)
/29633,825,300,114,114,700,748,351,602,688 (2^99)34,359,738,368524,288NoRIPE allocation to a provider (often)
/3279,228,162,514,264,337,593,543,950,336 (2^96)4,294,967,29665,536YesProvider allocation (RIPE default)
/364,951,760,157,141,521,099,596,496,896 (2^92)268,435,4564,096Yes
/40309,485,009,821,345,068,724,781,056 (2^88)16,777,216256Yes
/4419,342,813,113,834,066,795,298,816 (2^84)1,048,57616Yes
/481,208,925,819,614,629,174,706,176 (2^80)65,5361YesOne site or organisation (RIPE PI / assignment)
/5275,557,863,725,914,323,419,136 (2^76)4,096Yes
/564,722,366,482,869,645,213,696 (2^72)256YesSmall site or home (common provider assignment)
/60295,147,905,179,352,825,856 (2^68)16YesSome home broadband (16 LANs)
/6418,446,744,073,709,551,616 (2^64)1YesOne LAN or VLAN (needed for SLAAC)
/7272,057,594,037,927,936 (2^56)1/256 of a /64Yes
/80281,474,976,710,656 (2^48)1/65,536 of a /64Yes
/964,294,967,2961/4,294,967,296 of a /64YesEmbeds an IPv4 address (NAT64)
/11265,5361/281,474,976,710,656 of a /64Yes
/1202561/72,057,594,037,927,936 of a /64Yes
/124161/1,152,921,504,606,846,976 of a /64Yes
/12641/4,611,686,018,427,387,904 of a /64No
/12721/9,223,372,036,854,775,808 of a /64NoPoint-to-point link (RFC 6164)
/12811/18,446,744,073,709,551,616 of a /64YesOne host or loopback

Private and special ranges

IPv4

Special-purpose ranges
RangeNameWhat it is
255.255.255.255/32Limited broadcastEvery host on the local network
0.0.0.0/8This networkNot routed; 0.0.0.0 means "any address" in settings
10.0.0.0/8Private (RFC 1918)Office and home networks; not routed on the internet
100.64.0.0/10Shared address space (CGNAT)Used by providers behind carrier-grade NAT (RFC 6598)
127.0.0.0/8LoopbackThis computer
169.254.0.0/16Link-local (APIPA)Self-assigned when no DHCP server answers
172.16.0.0/12Private (RFC 1918)Office and home networks; not routed on the internet
192.0.0.0/24IETF protocol assignmentsSpecial uses such as DS-Lite
192.0.2.0/24Documentation (TEST-NET-1)For examples; never used on a network
192.88.99.0/246to4 relay (deprecated)Formerly anycast for 6to4
192.168.0.0/16Private (RFC 1918)Office and home networks; not routed on the internet
198.18.0.0/15BenchmarkingNetwork equipment testing (RFC 2544)
198.51.100.0/24Documentation (TEST-NET-2)For examples; never used on a network
203.0.113.0/24Documentation (TEST-NET-3)For examples; never used on a network
224.0.0.0/4MulticastOne-to-many traffic, such as IPTV and routing protocols
240.0.0.0/4ReservedFuture use; not usable on most systems

IPv6

Special-purpose ranges
RangeNameWhat it is
::/128UnspecifiedNo address; :: means "any address" in settings
::1/128LoopbackThis computer
::ffff:0:0/96IPv4-mappedAn IPv4 address written as IPv6
64:ff9b::/96NAT64IPv4 addresses reached through a NAT64 gateway
100::/64Discard onlyTraffic sent here is dropped (RFC 6666)
2001:db8::/32DocumentationFor examples; never used on a network
2001::/32TeredoIPv6 tunnelled over IPv4 UDP
2002::/166to4IPv6 tunnelled over IPv4 (largely retired)
3fff::/20DocumentationFor examples (RFC 9637)
fc00::/7Unique local (ULA)Private IPv6, like RFC 1918; usually fd00::/8
fe80::/10Link-localEvery IPv6 interface has one; not routed
ff00::/8MulticastOne-to-many traffic; replaces broadcast
2000::/3Global unicastPublic internet addresses

About this tool

A network is written as an address and a prefix length, such as 192.168.1.0/24: the first 24 bits name the network and the rest number the devices on it. The calculator works out where the network starts and ends, how many devices it holds, its subnet and wildcard masks, and the reverse DNS zone to ask your provider for.

It also splits a network into equal smaller ones (one per VLAN or site), turns a range of addresses into the fewest CIDR blocks for a firewall rule, and lists every IPv4 prefix length and the common IPv6 ones in reference tables.

Common questions

Why are two addresses lost in every IPv4 subnet?

The first address names the network and the last is the broadcast address, so a /24 has 256 addresses but 254 for devices. A /31 (a link between two routers) and a /32 (one host) are the exceptions.

What size of IPv6 network should a LAN use?

Always /64. Devices pick their own address within it (SLAAC), which needs the full 64 bits. A site usually gets a /48 or /56 from its provider, which holds 65,536 or 256 LANs.

What is a wildcard mask?

The subnet mask turned inside out: 255.255.255.0 becomes 0.0.0.255. Cisco access lists and OSPF use it to say which bits must match.

Which ranges can I use inside an office?

IPv4: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. IPv6: unique local addresses from fd00::/8, though most networks use the public prefix from their provider.